Cathode structure for electrolytic diaphragm cell



Feb. 3, 1970 w. w. RUTHEL ETA!- 3,493,437

CATHODE STRUCTURE FOR ELECTROLYTIC DIAPHRAGM CELL I Filed May 16, 1966 Patented Feb. 3, 1970 3,493,487 CATHODE STRUCTURE FOR ELECTROLYTIC DIAPHRAGM CELL Walter W. Ruthel, Niagara Falls, and Alvin T. Emery,

North Tonawanda, N.Y., assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed May 16, 1966, Ser. No. 550,287 Int. Cl. B01k 3/04 US. Cl. 204284 8 Claims ABSTRACT OF THE DISCLOSURE A cathode structure for a chlor-alkali type diaphragm electrolytic cell presenting a conductive metal enclosure having positioned therein a peripheral foraminous metal chamber, said chamber having in communication there with plural foraminous metal projections traversing the width of the cathode structure, said foraminous projections being substantially rectangular in cross section and having substantially 90 corners, wherein the attachment of said projections to the peripheral chamber also forms a substantially 90 angle at the point of junction.

This invention relates to electrolytic cells for the electrolysis of aqueous solutions and more particularly to the cathode structure of a diaphragm type electrolytic cell particularly suited for the electrolysis of aqueous alkali metal chloride-containing solutions.

Chlor-alkali diaphragm cells have been used extensively for many years for the production of chlorine, caustic and hydrogen. Over the years, such cells have been perfected to a degree whereby high operating efficiencies are obtained based on the electrical energy expended. Most recent developments in diaphragm chlor-alkali cells have been in improvements for increasing the production capacity of individual cells, thereby obtaining a higher pro duction rate for a given cell room area. Chlor-alkali cells have most recently been developed capable of utilizing over 55,000 amperes of current per cell. In order to obtain high efliciencies in chlor-alkali diaphragm cells of such high current capacities, comparable to the more conventional lower amperage cells of about 30,000 amperes or less, various structural improvements are best incorporated into these high amperage cells to maintain or increase their current and power efiiciencies. Mere enlargements of the component parts of such cells, while providing efficient cells, do not always provide the most favorable efficiencies, based on construction costs and operating performance.

With increasing sizes of electrolytic cells, difficulties are encountered in maintaining the relatively narrow tolerances in anode blade alignment with respect to the foraminous cathode structure. Higher capacity cells are substantially larger in size while the preferred spacing between the anode and cathode remains the same. If the distance between the anode and cathode is too little, elec trical shorting will occur; the cell becomes electrically inefiicient when the electrodes are too far apart. In order to obtain high efiiciencies, the relatively narrow toler ances in blade alignment should be maintained for the entire expanse of anode and cathode surfaces.

It is an object of the present invention to provide a cathode structure particularly suited for high amperage chloralkali cells, whereby the relatively narrow tolerances of anode and cathode distances can be more readily obtained. Another object of the present invention is to provide an improved cathode structure of increased structural strength, whereby misalignment due to warpage and flexing of the cathode structure is greatly reduced. A further object of the present invention is to provide an improved cathode structure which is more readily fabricated. These and other objects will become apparent to those skilled in the art from the description of the invention which follows:

In accordance with the invention, a cathode structure is provided for an electrolytic chlor-alkali diaphragm type cell comprising a conductive metal enclosure having positioned therein a peripheral foraminous metal chamber, said chamber having in communication therewith a plurality of foraminous metal projections traversing the width of said cathode structure, said foraminous projections being substantially rectangular in shape having substantially sharp, degree corners and wherein the attachment of said projections to said peripheral chamber forms a substantially sharp 90 degree angle therewith.

The present invention provides an improved cathode structure for diaphragm type electrolytic chlor-alkali cells by which accurate alignment of the cathode with the anode blades is more readily eflected and maintained. Additionally, the cathode structure can be fabricated at a lower cost while resulting in increased structural strength. A further asset of the present cathode structure is its elasticity when deflected and its resistance to permanent structural change when deflected.

The invention will be more fully described by reference to the drawing in which:

FIG. 1 is a plan view of the cathode structure in accordance with the present invention; and

FIG. 2 is an enlarged partial sectional elevation view of the cathode of FIG. 1 along plane 22, further illustrating the position of the anode blades and cell bottom in relation to the foraminous cathode projections.

Because the present invention may be used in many difierent electrolytic processes of which chlor-alkali electrolysis is of primary importance, the invention will be described more particularly with respect to such chloralkali diaphragm cell operation. However, such description is not to be understood as limiting the usefulness of the present invention, particularly in view of the fact that the present cell can be operated without the use of a diaphragm as described hereinafter.

The cathode section 10 of the present invention is comprised of an enclosure having sidewalls 14 forming preferably a rectangular shaped structure of a suitable size corresponding to the particular cell and capacity thereof, with which cell it is to be used, and a plurality of foraminous projections 18. Surrounding the enclosure at the top and bottom of sidewall 14 are flanges 12 and 13. Flanges 12 and 13 are utilized to more conveniently seal the cathode section in a watertight relationship in the assembled electrolytic cell. Flange 13 rests on gasket 30 which is between the cathode 10 and cell bottom 28. Flange 12 provides a contact plate on which the cell top (not shown) rests. Surrounding the internal portion of cathode 10 is peripheral chamber 16. Gas being liberated in the cathode section during the electrolysis is channeled across the foraminous projections 18 to the peripheral chamber 16 from whence it proceeds to gas withdrawal means 20.

Extending across cathode 10 is a plurality of foraminous projections 18. These are commonly called cathode fingers. The number of foraminous projections may vary widely, depending on the particular cell size, but commonly about 2 to or more, more preferably 5 to 50 and most preferably about 15 to 25 are present.

In the use of the present apparatus as a chlor-alkali diaphragm cell, an inert diaphragm is applied or deposited on the foraminous structure. The diaphragm which can be used to cover the screen or foraminous portion of the cathode is a fluid-permeable and halogen-resistant material. Preferably, the material is asbestos deposited in situ on the outer surfaces of the cathode or foraminous projections 18 and the peripheral chamber 16, the diaphragm material facing the anode blades. However, other types of diaphragms can be used depending on the reaction and reaction conditions contemplated within the cell. Other diaphragm materials such as those comprised of synthetic organic materials, such as Woven after-chlorinated polyvinyl chloride, polyvinylidene chloride, polypropylene, Teflon, and the like, may be used. These and other suitable materials are known to those skilled in the art. The cathode structure is adapted to permit use of all types of diaphragms including sheet asbestos, deposited asbestos and synthetics which can be in the form of woven fabrics.

The foraminous projections 18 and peripheral chamber 16 are preferably constructed of metal screen mesh which can also be perforated metal plating or the like foraminous structures. The metal parts of the cathode are of a conductive metal and preferably, are of relatively inexpensive loW-carbon steel. However, various other metals can be used such as titanium, nickel, chromium, copper, iron, tantalum and the like and alloys thereof, especially stainless steel and other chromium steels, nickel steels and the like. Also, various parts of the cathode can be constructed of copper or other low resistance metals to increase electrical conductivity. When copper or other low resistance metals are used, it is preferred to construct the reinforcing means 24 of such metals because the reinforcing means serve the dual function of conducting the electrical energy to the foraminous screen surfaces and strengthening the projections. Thus, increased electrical efiiciencies can be obtained in the use of the various more conductive metals and alloys.

The foraminous mesh screen 26 is preferably reinforced with reinforcing means 24. Reinforcing means 24 is preferably a corrugated sheet metal material which is preferably attached to the sidewall of the cathode on at least one side of the cathode. The foraminous mesh screen 26 is attached, as by welding, to the reinforcing means 24. As stated above, reinforcing means 24, when used, serves the dual function of both supporting and reinforcing the foraminous screen and further in conducting the electrical energy to the extremities of the cathode fingers.

The foraminous projections 18 are fabricated from lowcarbon steel mesh screen or the like as described, utilizing sharp bends so as to provide relatively sharp 90 degree corners 36 having a relatively small radius of curvature, e.g., less than about one centimeter and more preferably less than 0.8 centimeter radius for the outside radius. The radius of curvature is a means of measuring curves based on the radius of the are formed by the bend. The measurements given are for the radius of an outside arc, the inside arc having a correspondingly smaller radius depending on the foraminous metal thickness. The sharp 90 degree corners increase the structural strength of the cathode, particularly When used in connection with the reinforcing means 24. Although reinforcing means 24 is preferably a corrugated structure, other suitable reinforcing means such as bars, plates, and the like, can also be used.

In a like manner, the joints of the foraminous projec tions 18 with the peripheral chamber 16 are made at a relatively sharp 90 degree angle as described above. The foraminous projections 18 are conveniently attached, as by welding, to the foraminous section of the peripheral chamber while the reinforcing means 24 is preferably extended to, and attached to the sidewall of the cathode.

In the assembled cell, cathode section is positioned over cell bottom 28 in a manner whereby anode blades 22 project from cell bottom 28 upwards between foraminous projections 18. The alignment distance between the anode blade and the foraminous fingers is normally between about and of an inch. Therefore, as the height and width of the cathode structure increases, the criticality of having the anode and cathode functions in proper alignment with each other across the entire height and width of the electrode surfaces becomes increasingly difficult as the size thereof is increased. In the present invention these difiiculties are substantially reduced or eliminated and the desired cathode alignment with respect to the anode is more readily obtained. Thus, slight Warpages, flexing and the like in the foraminous projections previously resulted in extreme difficulties in maintaining proper distances between the anode and cathode over wide expanses, whereas the present invention overcomes these difficulties and provides the means for retaining the desired anode-cathode distance for the entire opposing anode and cathode surfaces by providing a more rigid structure which is resistant to permanent structural deflections.

The anode blades 22 are secured to cell bottom 28 by means of conductive metal 32. Conductive metal 32 is normally lead or other relatively low melting conductive metal material which can be readily molded about the anode blades. The particular metal utilized is one which will melt at a temperature below that at which the carbon or graphite anode blades are degraded. A sealing material 34, such as an inert organic polymer or resinous material, is applied over the conductive metal 32 to eliminate electrolytic attack by the electrolyte on the conductive metal during cell operation.

In the operation of an electrolytic cell using the present cathode structure as a chlor-alkali cell, an alkali metal chloride, for example, sodium chloride, is introduced into the cell as a brine stream of desired concentration. The brine level Within the cell is brought to a point above the anode blades Within the cell. By adjusting the level within the cell, the hydrostatic head or pressure exerted upon the diaphragm covering the foraminous cathode fingers is varied, thereby varying the flow of electrolyte through the diaphragm into the cathode compartment. Under normal operating conditions, the height of the brine above the anode blades is about 1 to 15 or more inches.

As previously stated, the cathode section of the present invention can be used in a cell used for the electrolysis of alkali metal chloride solutions, including not only sodium chloride but also potassium chloride, lithium chloride, rubidium chloride and cesium chloride. In the electrolysis using a diaphragm covering the foraminous cathode, caustic, chlorine and hydrogen are produced. Using certain modifications and changes in the method of reacting, such as by removing the diaphragm or further reacting the produced caustic and chlorine, alkali metal chlorates can also be produced by the present cell. Thus, in some instances, when used for the production of alkali metal chlorates, solutions containing both alkali metal chlorate and alkali metal chloride are recirculated to the cell for further electrolysis. In yet another modification, the present cathode structure can be utilized in a cell for the electrolysis of hydrogen chloride by electrolyzing hydrogen chloride in combination with an alkali metal chloride. Thus, the present cathode structure and cell is highly useful in these and many other aqueous electrolytic processes.

The above-described cathode section offers significant advantages when utilized as a cathode section of an electrolytic cell. A most important consideration is the extremely high electrical efiiciency in operation at unusually high current capacities of the order of 60,000 amperes and higher. Such high amperages provide for considerably greater productivity for a given cell room area. The novel structure of the cathode of the present invention provides improved control of structural tolerances, thereby permitting the practical operation of large electrolytic cells. In addition to being capable of operating at extremely high amperage capacities, the present cell can also be effectively operated at lower amperages, such as about 30,000 amperes .or less, and higher amperages upward to 100,000 amperes.

EXAMPLE A cathode for an electrolytic cell was constructed in accordance with the present invention as illustrated in the drawings. The cathode was of a size designed for Cathode Present Prior art type Deflection (in inches) ;2 %2 Force required (in pounds) 51 60 17 24 1 Too high to measure on instrument used. 2 Too low to measure on instrument used.

At deflections above about A inch, the prior art cathode structure tended to retain the deflection whereas the cathode of the present invention remained elastic at such deflections. The resistance to deflections in the present cathode design results in increased electrical efficiencies, especially in extended usages, due to the increased ability to maintain the desired anode and cathode distances.

While there have been described various embodiments of the present invention, the apparatus described is not intended to be understood as limiting the scope of the invention. It is realized that changes therein are possible. It is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner. It is intended to cover the invention broadly in whatever form its principles may be utilized.

What is claimed is:

1. A cathode structure for a chlor-alkali type diaphragm electrolytic cell comprising a conductive metal enclosure having positioned therein a peripheral foraminous metal chamber, said chamber having in communication therewith a plurality of foraminous metal projections traversing the width of said cathode structure, said forarninous projections being substantially rectangular in shape and having substantially sharp 90 degree corners and wherein the attachment of said projections to said peripheral chamber forms a substantially sharp 90 degree angle therewith.

2. The apparatus of claim 1 wherein the foraminous projections are steel screen mesh.

3. The apparatus of claim 1 wherein the foraminous projections are substantially the same height as said cathode structure.

4. The apparatus of claim 1 wherein the cathode structure comprises about 5 to about foraminous projections.

5. The apparatus of claim 1 wherein the sharp corners have an outside radius of curvature of less than one centimeter.

6. The apparatus of claim 1 wherein the relatively sharp corners have an outside radius of curvature of less than about 0.8 centimeter.

7. The apparatus of claim 1 wherein the foraminous projections are internally reinforced with reinforcing H12IHS.

8. The apparatus of claim 3 wherein the reinforcing means is a corrugated plate extending substantially across said cathode structure, said corrugated plate being substantially the internal height of said projection.

References Cited UNITED STATES PATENTS 1,855,497 4/1932 Stuart 204-283 2,409,912 10/1946 Stuart 204-266 2,987,463 6/1961 Baker et al. 204266 3,342,717 9/1967 Leduc 204265 JOHN H. MACK, Primary Examiner D R. JORDAN, Assistant Examiner US. Cl. X.R. 204-266 

